Traditionally, scintillation detectors have been used in research applications in laboratories but they are more recently finding important applications in industry. A particular problem with scintillation detectors using photomultipliers is that they are prone to gain drift which means that in continuous use the calibration may change significantly. This may require periodically stopping the industrial measurement and moving the detector to a re-calibration location which is a problem requirement. The scintillation detectors typically used to implement the measuring system described in New Zealand patent 213777/214666 also employ pulse shape discrimination to separate neutron and gamma events which is a temperature dependent process. A procedure adopted to minimise gain stabilisation problems is to control the temperature of the detector, but in practice gain changes can be expected to occur.